Process for providing a pilot aided phase recovery of a carrier

Abstract

Providing a pilot aided phase recovery of a carrier of an input digital signal Zk having signal fields of Ls symbol signals, LP pilot symbol signals ZP(k) and (Ls−LP) data symbol signals Zd(k), by for each signal field:calculating an unwrapped pilot phase estimate {circumflex over (θ)}f(P)(l);initiating with {circumflex over (θ)}f(P)(l) a first digital phase locked loop implementing a phase estimate algorithm and calculating a forward phase trajectory {circumflex over (θ)}F(k) from Zd(k), ks varying between 1 and Ls−LP over the data field (l), {circumflex over (θ)}F(P)(l) having Ls−LP forward phase estimates {circumflex over (θ)}F(ks);and initiating with {circumflex over (θ)}(P)f(l+1) a second digital phase locked loop, implementing a phase estimate algorithm and calculating a backward phase trajectory {circumflex over (θ)}B(ks) from Zd(k), ks varying between Ls−LP and 1 over said data field (l), {circumflex over (θ)}B(ks) having Ls−LP backward phase estimates {circumflex over (θ)}B(ks); andfrom said phase trajectories calculating a phase correction (e−j{circumflex over (θ)}(ks)).

Description

FIELD OF THE INVENTION[0001]The present invention relates to a pilot-aided carrier synchronization scheme particularly suited to broadband satellite communication systems, as the ones concerning the new DVB-S2 standard.BACKGROUND OF THE INVENTION[0002]It has been shown in the article by A. GINESI and R. DE GAUDENZI “Carrier Phase Synchronization Techniques for Broadband Satellite Transmissions” DVB-S2 Technical doc, Geneva, 21 Mar. 2003 that classical techniques for carrier phase recovery in the presence of a strong phase noise as the one specified by the DVB-S2 committee, are not effective as they are affected by both excessive jitter as well as cycle slips. Other pilot aided techniques, as described in the publication by HUGHES Networks Systems “Carrier Synchronization Solution for DVB-S2 Modem” DVB-S2 Technical doc, Geneva, 15 Jun. 2003 are more effective but they are much more complex and yet have to show a feasibility over the whole signal-to-noise ratio range required by the D...

AI Technical Summary

Benefits of technology

[0004]As an example, the currently deployed LNB's (Low Noise Blocks) in the digital TV broadcast receiver terminals (DVB-S receivers) belong to this class of relatively low cost components. Re-using this low cost technology, the DVB-S2 standard aims at providing an increase of user data rates in the order of 30%, by exploiting state-of-the-art FEC (Forward Error Correction) techniques. As a result, the signal to-noise (SNR) ratio operating point of a given modulation and coding rate format is lowered thus stressing the operation of the carrier synchronization circuit. Classical synchronization schemes such as in the above identified publication by A. GINESI and R. DE GAUDENZI do not provide sufficient performance when in presence of the phase and thermal noise levels of the DVB-S2 environment, especially for modulation formats with 8 and 16 points. In fact, as shown in this publication, in these conditions the synchronizer undergoes a number of cycle slips in a relatively short time, and the phase jitter results to be in excess with respect the desired target. The proposed algorithms make use of regularly inserted pilot symbols with a total overhead around 2%. They provide a good carrier frequency and phase estimate with low jitter and no cycle slips. Furthermore, they are (at least for a set of the proposed algorithms) completely data modulation independent as they do not make any use of the transmit data. According to one of the proposed techniques, the carrier phase estimate is obtained by an optimum (in the minimum mean square error sense) interpolation of maximum likelihood pilot-based estimates, while the carrier frequency is obtained by holding the pilot-based estimates that are given by a simple delay-and-multiply PLL.

[0005]The synchronization schemes according to the present invention can also be advantageously applied to modulation formats that are difficult to synchronize as well as very sensitive to a carrier phase jitter as the non-linearity friendly 16-APSK and 32-APSK constellations. Also, the complexity of the proposed synchronizers is low when compared to other techniques such as in the above-referenced publication by HUGHES Networks Systems and the adaptation of frame-dependent modulation formats (as required in the Unicast application of DVB-S2) does not require any synchronizer re-configuration as opposed to the techniques in said publication by HUGHES Networks Systems thus easing the demodulator operations.

[0007]A number of algorithms are available in literature to address the issue of carrier phase recovery (see the book by U. MENGALI and A. N D'ANDREA “Synchronization Techniques for Digital Receivers” 1997—Plenum Press—New-York for a comprehensive literature review) for different modulation schemes. However, due to the recent findings in channel coding theory and the use of higher carrier frequencies, the need to study novel and more efficient carrier phase estimate techniques has received a new boost. In fact, since the introduction of Turbo codes (see for example C. BERROU et al: Near Shannon limit Error-Correcting Coding and Decoding: Turbo Codes”—Proceedings 1993 Int Conf. Comm. pages 1064-1070), the operating signal-to-noise ratios (SNR's) at which the synchronizers have to be able to work have considerably lowered, thus stressing their jitter performance.

Problems solved by technology

This situation is typical of the consumer market where due to strong cost restrictions, low quality components have to be chosen.

Classical synchronization schemes such as in the above identified publication by A. GINESI and R. DE GAUDENZI do not provide sufficient performance when in presence of the phase and thermal noise levels of the DVB-S2 environment, especially for modulation formats with 8 and 16 points.

Also, the complexity of the proposed synchronizers is low when compared to other techniques such as in the above-referenced publication by HUGHES Networks Systems and the adaptation of frame-dependent modulation formats (as required in the Unicast application of DVB-S2) does not require any synchronizer re-configuration as opposed to the techniques in said publication by HUGHES Networks Systems thus easing the demodulator operations.

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